Method and apparatus for de-electrifying insulative materials

ABSTRACT

METHOD AND APPARATUS FOR DE-ELECTRIFYING INSULATIVE MATERIAL MOVING PAST IONIZING ELECTRODES BY SUPPLYING A DE-ELECTRIFYING WAVEFORM HAVING AN IONIZATION PORTION AND A DAMPED PORTION TO THE IONIZING ELECTRODES. THE IONIZATION PORTION OF THE DE-ELECTRIFYING WAVEFORM INCLUDES ALTERNATE POLARITY PULSES HAVING AN AMPLITUDE TO IONIZE A GASEOUS MEDIUM SURROUNDING THE IONIZING ELECTRODES, AND THE DAMPED PORTION OF THE DE-ELECTRIFYING WAVEFORM HAS AN AMPLITUDE INSUFFICIENT TO IONIZE THE GASEOUS MEDIUM.   D R A W I N G

Feb. 13, 1973 G. P. WEBER ET AL 3,716,754

METHOD AND APPARATUS FOR DEELECTRIFYING INSULATIVE MATERIALS Filed Sept. 10, 1971 VOLTAGE H6 1 3 Sheets-Sheet l vn l\ f\ [\UAvAUA A n V A V U HME n 8 oscmmmz I INVENTORS, 6w P401 W555? BY A'rrmmnm METHOD AND APPARATUS FOR DE-ELECTRIFYING INSULATIVE MATERIALS Filed Sept. 10, 1971 Feb, 13, 1973 P. WEBER ETAL 3 Sheets-Sheet 2 PU LSE GENERATiNG C\\2CU \T VOLTAGE INVENTORS,

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METHOD AND APPARATUS FOR DE-ELECTRIFYING INSULATIVE MATERIALS Filed Sept. 10, 1971 3 Sheets-Sheet 5 E [6 j? 5 26 PULSE GENERM'WG CHZCLHT K\LO\/OLTS 6 \,5oo k \,OOO

RESlDUAL HELD 5 \O \5 '20 "L5 30 vous :UPPLY VOLTAGE INVENTORSI 60y P404 W555 p/f/l/FPE Mwffismres ATTORNEYS "United States Patent ()1 fice 3,716,754- Patented Feb. 13, 1973 3,716,754 METHOD AND APPARATUS FOR DE-ELECTRIFY- ING INSULATIVE MATERIALS Guy Paul Weber, 25 Rue Verdier Monetti, 76 Arques la Bataille, France, and Philippe Marie Deshayes, Avenue des Canadiens, 76 Neuville les Dieppe, France Filed Sept. 10, 1971, Ser. No. 179,339

Int. Cl. H01t 19/00; H05f 3/00 US. Cl. 317-2 F 17 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for de-electrifying insulative material moving past ionizing electrodes by supplying a de-electrifying waveform having an ionization portion and a damped portion to the ionizing electrodes. The ionization portion of the de-electrifying waveform includes alternate polarity pulses having an amplitude to ionize a gaseous medium surrounding the ionizing electrodes, and the damped portion of the de-electrifying waveform has an amplitude insufficient to ionize the gaseous medium.

BACKGROUND OF THE INVENTION Field of the invention The present invention pertains to the de-electrifying of insulated materials and, more particularly, to the de-electrifying of insulative materials moving past ionizing electrodes.

Discussion of the prior art Plastic materials and more generally all electrical insulative supports covered with a dielectric material are subject to become electrified during treatment and handling; that is, such materials are easily electrically charged. The electrification of such materials is disadvantageous in that it causes the materials to adhere to one another and other materials and in many cases causes deformation or bending of the material. Furthermore, the electrification attracts dust particles, and this is entirely unacceptable for certain applications such as the use of insulating films for condensers, as supports for magnetic tapes and in the graphic arts.

The electrical charges accumulated on the insulative materials may be in the form of inactive dipoles distributed in the material so as not to generate any outside field, unbalanced doublets distributed on the surface of the material, neutralized free charges carried on the surface of the material or active dipoles made up of polar molecular chains inside the material. The resulting field from the presence of surface doublets normally influences only limited areas; however, this field is responsible for the adherence of surfaces of films in contact and for the adherence of dust particles to surfaces of insulative material. The latter two mentioned types of charges normally accumulated in insulative materials cause resulting active outside fields to attract particles; and, accordingly, these types of charges can be detected by electrometers.

In the past in order to de-electrify insulative materials, metal conductors were arranged in the form of wreathes, brushes or the like to ground the surface of the materials; however, de-electrification in this manner has not been acceptable in that de-electrification is only momentarily effected and is directed only to surface charges.

Another known manner of de-electrifying insulative materials is based on the neutralization of electrostatic charges carried by the materials by adding thereto additional ions to saturate unbalanced doublets, connect active dipoles and naturalize free charges thus cancelling any active outside fields. In order to implement this method of de-electrification, ionizing electrodes are supplied with low frequency, high voltage sine wave alternating current in order to provide ionized or charged areas to which the material is exposed; however, this implementation has not been effective or acceptable in that the ions, which have acquired a certain kinetic energy during a half cycle, are subjected to an opposite force during the following half cycle. Consequently, the ions cannot easily escape the electrode in order to reach the surface of the material to be de-electrified.

In order to overcome this problem it has been proposed to supply the ionizing electrodes with high voltage, half cycle, alternating current with amplitude modulation at a frequency of generally 50 Hz. When the amplitude is small, the ions can be free from the alternating field; however, unless the speed at which the material passes the electrodes is extremely slow, alternating charged and discharged bands will exist on the material. These bands are spaced according to the ratio of the passing speed of the material and the frequency of the power supplied.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide method and apparatus for uniformly de-electrifying insulative materials by the addition of ions while moving the materials at high speeds.

The present invention is generally characterized in a method of de-electrifying an insulative material including moving the insulative material past ionizing electrodes and supplying a periodic electrical waveform to the ionizing electrodes, the waveform including an ionization portion having an amplitude suflicient to ionize the gaseous medium surrounding the ionizing electrodes followed by a damped portion having an amplitude insufiicient to ionize the gaseous medium. The present invention is further generally characterized in apparatus for de-electrifying an insulative material including an oscillator for providing the above described electrical waveform.

Yet a further object of the present invention is to regulate the amplitude of a damped alternating waveform applied to ionizing electrodes in order to control the amount of de-electrification of an insulative material.

Another object of the present invention is to utilize a high frequency alternating waveform with a high energy gradient prolonged by a damped wave having a low amplitude to de-electrify insulative materials moving at great speeds.

A further object of the present invention is to utilize a damped alternating signal to energize ionizing electrodes in order to provide a high energy gradient resulting in great instantaneous power to'impart large kinetic energy to the ions.

Another object of the present invention is to provide a method for continuously de-electrifying insulative materials by forming positive and negative ions in response to an electrical waveform defining an alternating signal formed by a series of damped pulses.

The present invention has another object in that a damped alternating waveform is utilized to energize ionizing electrodes with the waveform having a large decaying or damping time to provide sufficient time for the ions to escape from the electrodes.

Yet a further object of the present invention is to utilize a damped alternating waveform to energize ionizing electrodes with the waveform having a sufficiently high frequency to cause ion discharge at a rate compatible with increased speed of passing insulative material.

Another object of the present invention is to de-electrify an insulative material by utilizinga de-electrifying waveform having a period compatible with the nature of the gas to be ionized.

- Thepresent invention has another object in that a deelectrifying waveform is utilized for de-electrification of insulative materials with the waveform providing high momentary energy prolonged by a damped portion having a high frequency with a low amplitude without opposing the movement of ions away from the electrode while preventing the ions from recombining for a sufficient time in order to permit the ions to be attracted by the electric field created by the charges carried by the insulative material.

Some of the advantages of the present invention over the prior art are that ions of opposite polarities are produced in suflicient amounts to cancel electrostatic charges carried both on the surface and in an insulative material, the field which creates the ions is greatly reduced by damping for a suflicient time to enable the ions to reach the insulative material, a relatively low frequency alternating waveform is provided in order to overcome the inertia of relatively heavy positive and negative ions while developing a high gradient or energy in a very-short time, the method and apparatus of the present invention may be utilized to treat insulative materials moving at speeds greater than 400 meters per minute, insulative materials of varying widths may be uniformily treated in that the length of the ionizing electrode is not limited, and the amplitude of the de-electrifying waveform can be adjusted to control the amount of de-electrification of passing insulative material.

Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 4 are graphical representations of 'voltage plotted against time for an electrical waveform to be supplied to ionizing electrodes in accordance with the present invention.

FIG. 2 is a schematic diagram of apparatus for deelectrifying an insulative material in accordance with the present invention.

FIG. 3 is a schematic diagram of a preferred embodiment of apparatus for de-electrifying an insulative material in accordance with the present invention.

FIG. 5 is a schematic diagram of a modification of the apparatus of FIG. 3.

FIG. -6 is a graphical representation of the residual field obtained with the apparatus of FIG. 5 plotted against the supply voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrical waveform to be supplied to ionizing electrodes in accordance with the present invention is illustrated in FIG. 1 with the voltage of the waveform plotted against time. The period of the waveform is designated T, and the waveform includes an ionization portion dur ing time period t followed by a damped portion during time period t The ionization portion of the waveform is desirably as short as possible such that the frequency is extremely high in order to create an energy gradient of great magnitude. In any case, time t should not be greater than one half of the period T. The damped portion of the waveform has a substantially reduced decaying amplitude relative to the amplitude of the ionization portion of the waveform and has a frequency greater than the frequency of the ionization portion of the waveform. It is preferable to maintain the frequency of the damped portion of the waveform between 1000 and 3000 Hz. The time period t of the damped portion of the waveform is determined by the period T and the time t of the ionization portion of the waveform.

The amplitude A of the ionization portion of the waveform should be greater than the voltage required to ionize the gas surrounding the ionizing electrodes but less than a voltagewhich would result in sparking at the ionizing electrodes. The voltage amplitude A must be determined in accordance with the geometry of the ionizing electrodes and ambient conditions including the type of gas surrounding the ionizing electrodes. When the gas to be ionized is dry air, the minimum ionizing voltage is nornially within the range of from 4000 to 6000 volts.

The amplitude D of the initial cycle of the damped portion of the waveform should be greater than about 500 to 1000 volts; however, amplitude D must be mtaintained below the ionizing voltage.

Apparatus according to the present invention is illustrated in FIG. 2 and includes an oscillator 10 for supplying the de-electrifying waveform of FIG. 1 on an output 12 relative to ground and ionizing electrodes 14 and 16 disposed Within a grounded shield 18. An insulative material 20 is moved past ionizing electrodes 14 and 16 to be de-electrified by the gas ionized by the electrodes.

Ionizing electrodes 14 and 16 are preferably of the corona discharge type; however, any device capable of producing ions may be used with the present invention. It has been found when using corona discharge electrodes for de-electrifying the insulative material that it is desirable to position the electrodes on only one side of the material without utilizing counter-electrodes on the opposite side of the material. To increase de-electrification in order to permit increase of the speed of the insulative material, a plurality of ionizing electrodes may be connected in parallel and disposed transversely to the direction of travel of the insulative material on the same side of the insulative material or on opposite sides of the insulative material as long as the ionizing electrodes are not positioned opposite each other.

Since ionization is initiated by the existence of a certain voltage between the ionizing electrodes and ground, ionization intensity is increased by completely enclosing the field with the shield 18 around the ionizing electrodes 14 and 16, and the design of the shield and electrodes relative to spacing, configuration and size can be determined for optimum results by conventional techniques normally used in practice. However, since the distribution of ionization nodes along a wire or electrode varies with supply voltage, it is preferable to position at least two ionizing electrodes in parallel in order to obtain a uniform distri: bution of. ions in the space surrounding the electrodes and defined by the shield and the insulative material. In this manner, the amplitude of the supplied voltage may be adjusted for optimum results.

A preferred embodiment of the oscillator 10 is illustrated in FIG. 3 and includes a pulse generating circuit 22 for providing trigger pulses to a pair of controlled rectifiers orswitches 24 and 26. The cathodes of controlled rectifiers 24 and 26 are grounded, and the gates of the controlled rectifiers receive trigger pulses on outputs 28 and 30, respectively, from pulse generating circuit 22. The anode of controlled rectifier 24 is connected with a positive terminal 32 of a source of direct current through a resistor 34, and the anode of controlled rectifier 26 is connected with terminal 32 through a primary winding 36 of a tranformer 38 having a secondary winding 40. The anodes of controlled rectifiers 24 and 26 are connected by a capacitor 42.

Controlled rectifiers 24 and 26 may be silicon controlled recti'fiers, transistors, or any other similar rectifying device capable of being controlled at a gate electrode, and pulse generating circuit 22 may include any suitable pulsing circuitry such as interconnected monostable multivibrators to provide pulses on outputs 28 and 30 with the timing required to generate the waveform of FIG. 1.

The generating of the de-electrifying waveform of FIG. 1 will be described with respect to FIG. 4 wherein the waveform is plotted as voltage against time. The period T is defined as the time between T and T the time period t of the ionization portion of the waveform is defined asthe time between T and T and the time period t; of the damped portion of the waveform is defined as the time between T and T "In operation, at time T both controlled rectifiers 24 and 26 are'non-conductive with controlled rectifier 26 having just been deenergized by the current through primary winding' 36 that results in the trailing positive going pulse of the ionization portion of the waveform coupled with the trailing edge of the trigger pulse to controlled rectifier 26 which terminates at T With both controlled rectifiers 24 and 26 non-conductive the voltage signal re sponsive to the discharging of capacitor decays as illustrated between T and T At time T at triggerpulse is supplied on output 28 to render controlled rectifier 24 conductive; however, capacitor 42 is charged in 'a direction such that the conduction of controlled rectifier 24 has no appreciable effect on current throughth'e primary winding 36. Thus, the deelectrifying waveform is not affected by the conduction of controlled rectifier 24 but a charge does start to buildup (in capacitor 42. V

At time T a'trigg'er pulse is'supplied on output 30 to'render controlled rectifier 26 conductive, and capacitor 42 discharges through controlled rectifiers 24 and 26 to render controlled rectifier 24 non-conductive. The conduction of controlled rectifier 2-6 effectively grounds the junction between primary winding 36 and capacitor 42 to establish a ringing circuit as current issuddenly drawn through primary winding 26 which can oscillate only in accordance with the parameters of the ringing circuit, particularly, the capacitance of capacitor 42. Between time T and T; controlled rectifier 24 remains non-conductive and controlled rectifier 26 remains conductive such that the ringing set up in the circuit is damped and has a frequency greater than the frequency of the ionization portion of the waveform.

At time T a trigger pulse is supplied on output 28 to render controlled rectifier 24 conductive such that capacitor 42 discharges through controlled rectifiers 24 and 26 to render controlled rectifier 26 non-conductive. The junction between resistor 34 and capacitor 42 is now effectively at ground, and a large current is drawn through primary winding 36 to provide an ionizing pulse between times T and T from secondary winding 40 to ionizing electrodes 14 and 16. Capacitor 42 is charged during this pulse, and the current through the primary winding is reduced as the valtage across the secondary winding passes through zero at time T .Controlled rectifier 26 is triggered at time T by a pulse at output 30, which pulse does not terminate until T which corresponds with time T at the start of the next waveform. With controlled rectifier 26 conducting, capacitor 42 discharges through controlled rectifiers 24 and 26; however, due to the large charge on capacitor 42, controlledrectifier 24 is rendered non-conductive before capacitor 42 is completely discharged. Thus, capacitor 42 discharges through primary winding 36 and resistor 34 to continue oscillation while reversing the polarity of the ionization portion of the waveform.

Between times T and T capacitor 42 is successively charged and discharged through the inductance of primary winding 36 in order to provide an alternating signal having a great voltage amplitude due to the matching of the capacitor 42 and the primary winding 36.

[At time T controlled rectifier 26 is deenergized as above described at time T and the waveform cyclically repeats itself.

Thus, by selectively grounding the junctions between resistor34 and'capacitor 42 and between primary winding 36 and capacitor 42 by triggering control rectifiers 24 and 26, respectively, the de-electrification waveform of FIGS. 1 and 4 may be, provided with'the utilization of a DC source. As mentioned above, the resulting de-electrifying waveform has an ionization portion consisting of a positive pulse followedby a negative pulse, and this ionization portion of the waveform is operative to raise the ionizing electrodes 14 and 16 of the ionizing potential in order to expose the passing insulative material to ions formed in a gas in order to de-electrify the material. After the negative pulse, the de-electrifying waveform is damped such that the waveform decays with an amplitude less then the ionizing potential, and there is no opposite force applied to the ions to impede their escape form the ionizing electrodes. The frequency of the positive and negative pulse cycle of the ionization portion of the wave form is high in order to permit the insulative material 20 to pass by the ionizing electrodes at great speeds.

The ionizing electrodes 14 and 16 may be disposed in air or other gaseous media. For example, the ionizing electrodes may be disposed in a nitrogen atmosphere which is extremely advantageous in the de-electrification of insulative materials coated with products in solution in organic solvents since the danger of fire is eliminated. De-electrification according to the present invention is increased in effectiveness by disposing the ionizing electrode in a gaseous media having relatively low molecular coated with an insulative dielectric material such as for example fabrics, unwoven materials, fiber yarns, sheets and generally all textiles regardless of whether they are coated. The method and apparatus is also suitable for yarn, fibers and roves, individually.

A particularly advantageous use for the method and apparatus of the present invention is to de-electrify papers of all types during various stages of fabrication to obviate, for example, the present requirement of moistening papers to de-electrify them. The method and apparatus of the present invention may further be applied to glossy or coated papers of any type, to plasticized papers and to papers having a plastic base. De-electrification by the method and apparatus of the present invention is extremely advantageous in that such de-electrification is relatively permanent in comparison with de-electrification accomplished by means of prior art methods. For example, cutting of an insulative material de-electrified in accordance with the present invention will not be sufiicient to recharge the insulative material; and, thus, an insulative material may be de-electrified prior to cutting for sizing and other purposes even when the insulative material is of a thickness of only a few microns. Deelectrification according to the present invention permits extremely thin films to be continuously unwound from reels whereas in prior art processes when such a film was unwound, it would immediately be pulled back onto the reel by electrostatic attraction overcoming the force of gravity.

The electrification or static charging of insulative materials is normally manifested by attraction of dust, difficulty in handling, adhering of the material to itself and other insulative surfaces, and glow discharge when the electrostatic voltage is increased to sparking potential thereby creating a dangerous situation for personnel and a high risk of fire. These manifestations are utilized in the following examples to indicate the different effects obtained with electrified and de-electrified insulative materials.

An electrified insulative material held a few centimeters above cigarette ashes will attract the ashes such that the ashes adhere thereto; however, a de-electricfied insulative material "can be held within a few millimeters of the ashes without having any trace of the ashes adhere thereto. A flexible insulative material, such as film, cloth, paper or the like, when positioned closed to an insulative vertical metal surface, will adhere strongly to the surface if the insulative material is electrified; however, if the insulative material is de-electrified, it will slide freely along the surface. If an electrified light plastic film of only a few microns thickness is unwound downwardly from a reel to a length of approximately 15 centimeters, the film will rewind itself around the reel; however, if the plastic film is de-electrified, it will hang vertically under its own weight regardless of how light the plastic film is. Of course, as is well known, the external field resulting from the electrification of an insulative material can be measured by subjecting the material to signals from an RF source. I

The present invention will now be described by reference to the following specific examples. It is to be understood that such examples are presented for purposes of illustration only, and the present invention is not meant to be limited thereby.

EXAMPLE 1 A film of polyethylene terephthalate,.50 microns thick and 2,400 mm. wide, is cut in rolls widthwise on a conventional machine operating at a speed of 300 m./minute. Under normal conditions, the film, which is strongly charged with electricity during prior handling, attracts any dust in the surrounding air. After de-electrification, before cutting, in accordance with the .present invention The method and apparatus according to the present invention as described above is extremely effective and can produce total de-electrification of insulative. materials; however, total de-electrification is not always desirable due to the effect on winding characteristics especially with respect to plastic films and in particular extremely thin films. That is, conventional winding devicesare designed to accommodate films that are slightly or-not at all de-eleetrified; and, accordingly, reels are not available utilizing a corona discharge electrode of 2,406 mm. in

length, no dust adheres to the film, and the film remains perfectly inert when subjected to the cigarette ash test.

EXAMPLE 2 The electric field produced at the end of the fabrication operations by a reel of a polyethylene terephthalate film, 34 microns thick, 1200 meters long and 140 cm. wide, as measured with a radio-emitting source, is about 1.5 million volts. Upon being de-electrified in accordance with the present invention and rewound, the same reconstituted reel presents only an electric field of 600 volts, measured under similar conditions.

EXAMPLE 3 A polypropylene film 6 microns thick is cut into narrow strips by a machine. This extremely flexible film is very light and hard to handle upon leaving the machine, because it strongly adheres to itself and surrounding surfaces. After de-electrification in accordance with the present invention, a length of such film of some meters suspended vertically, hangs absolutely straight, even if approached by other surfaces, and responds positively to the other control tests.

EXAMPLE 4 Sheets of synthetic paper for printing, made from a Y I sheet of non-Woven fibers, are stacked. These sheets, out under normal conditions, are strongly charged with electricity, and this electrification causes the sheets to stick together such that the suction device of a printing press takes several of them at a time which inhibits operation. When such sheets are de-electrified after cutting in accordance with the present invention, the sheets are picked up individually by the suction device for delivery to the printing press.

EXAMPLE 5 for use with completely de-electrified films since the film windings no longer adhere to one another and will slide. The windings, thus formed, are not cohesive, have edges which are not precisely aligned, and have a tendency to unwind. In view of the above, it is highly advantageous to be able to regulate the amount of de-electrification of insulative materials in order to provide both suflicient deelectrification of the material while permitting good winding characteristics.

Accordingly, a modified embodiment of the present invention is illustrated in FIG. 5 and differs from the apparatus of FIG. 3 primarily in thatthe amplitude of the de-electrifying waveform and particularly the ionization portion thereof, can be regulated'bythe number of ions emitted'by the ionizing electrodes; and, accordingly,- the rate of de-electrification of passinginsulative material may be controlled. As mentioned above, theamplitude of the ionization portion of the de-electrifying waveform must be maintained lower than a spark potential which could cause sparking between the ionizing electrodes and higher than the ionization potential which is determined by the geometry of the ionizing electrode structure and amplitude including the type of gaseous media to be ionized. Thus, by controlling the amplitude of the alternating pulses of the ionization portion of de.-clectrifying waveforms, it is possible to control the amount of deelectrification of the insulative material.

The amplitude of the de-electrifying waveform is a function of the supply voltage applied to the ringingcir cuit and controlled rectifiers; and, thus, in order to permit regulation of the de-electrification of a passing insulative material, the embodiment of FIG. 5 includes an autotransformer 42 whichhas a movable tap 44 and terminals 46 and 48. Asource 50 supplies a high voltage AC signal to terminals 46 and 48 of auto-transformer, and the output from auto-transformer 42 is supplied to a full wave recti fier 52 through tap 44'and terminal 46. Thus, the positive voltage on terminal 32 is dependent upon the position of tap 44 and can be increased or decreased as desired.

The components ofthe-oscillator for supplying the de-elec'trifying waveform are the same as those inthe embodiment of FIG'. 3'. and arefgiven identical reference. numbers and not described again. Furthermore, the operation of the embodiment of FIG..5 is exactly the same as that described with respect to FIGS. 3 and 4 withthe exception thatthe amplitude ofthe alternating polarity' pulse of the. ionization portion of thede-electrifying wave; form may be varied by changing the position of the tap 44 on auto-transformer 42..

.With reference to FIG. 6 the results obtained by use of the embodiment of FIG. Swill be more fully, appreciated. Windings of polyethylene terephthalate film, 34 microns thick, meters long by centimeters wide were fabricated and, after fabrication, the electric field measured with the use of an rf source was 1.5 million volts. A certain number of these windings were then deelectrified in accordance with the present invention 'by moving-them at the same speed past the ionizing electrodes with the supply voltage at terminal 32 being regulated manually by movement of tap 44 between 5 and 30 volts in order to provide the ionization portion of the de-electrifying waveform with amplitude from the minimum ionization voltage to the maximum sparking voltage.

In the graphical representation of FIG. 6 the residual field remaining in the de-electrified insulative material is plotted along the abscissa while the supply voltage is plotted along the ordinate; and, as examination of the plot of FIG. 6 verifies, when the supply voltage is at volts which corresponds to the minimum ionization voltage, the residual field is very close to the electrical field of the insulative material prior to de-electrification indicating that de-electrification has been insignificant. As the supply voltage increases, however, de-electrification is substantially increased such that at the sparking voltage, which occurs when the supply voltage is at approximately 30 volts, the de-electrification is complete for all practical purposes.

Accordingly, the apparatus of FIG. 5 may be utilized to provide any desired residual field within an insulative material to be de-electrified such that any insulative material may be provided with the exact characteristics re quired for optimum use in a particular application.

The method of the present invention as described above effectively includes the steps of moving an insulative material past ionizing electrodes disposed in a gaseous media and supplying a periodic electrical Waveform to the ionizing electrodes, the electrical waveform including an ioniza tion portion having an amplitude sufficient to ionize the gaseous media and a damped portion having an amplitude insufficient to ionize the gaseous media. The electrical waveform is periodic and has a frequency sufficiently high to de-electrify insulative material moving past the ionizing electrodes at great speeds.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter described above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A method of de-electrifying an insulative material comprising the steps of moving the insulative material past ionizing electrode means in a gaseous medium; and

supplying a periodic electrical waveform to the ionizing electrode means, the electrical waveform including an ionization portion having an amplitude sufficient to ionize the gaseous medium followed by a damped portion having an amplitude insufficient to ionize the gaseous medium.

2. The method as recited in claim 1 wherein said supplying step includes forming the ionization portion of the electrical waveform with alternating polarity pulses each having an amplitude to ionize the gaseous medium.

3. The method as recited in claim 2 wherein said supplying step further includes forming the damped portion of the electrical waveform with an alternating signal having a frequency greater than the frequency of the alternating pulses of the ionization portion of the electrical waveform.

4. The method as recited in claim 3 wherein said supplying step includes selectively controlling the amplitude of the alternating polarity pulses.

5. The method as recited in claim 3 wherein said alternating polarity pulses consist of a single pulse of a first polarity followed by a single pulse of a second polarity.

6. The method as recited in claim 1 wherein said supplying step includes selectively controlling the amplitude of the ionization portion of the electrical waveform.

7. The method as recited in claim 1 wherein said controlling step includes controlling the amplitude of the ionization portion of the electrical waveform between the ionizing potential of the gaseous medium and a sparking potential of the ionizing electrode means.

8. Apparatus for the de-electrifying insulative materials comprising ionizing electrode means disposed in a gaseous medium and adapted to have an insulative material to be deelectrified moved thereby; and

oscillator means for supplying a periodic electrical Waveform to said ionizing electrode means, said electrical waveform including an ionization portion having an amplitude sufficient to ionize said gaseous medium followed by a damped portion insuflicient to ionize said gaseous medium.

9. The apparatus as recited in claim 8 wherein said oscillator means includes means for forming said ionization portion of said electrical waveform with alternating polarity pulses each having an amplitude sufficient to ionize said gaseous medium.

10. The apparatus as recited in claim 9 wherein said oscillator means includes switch means for controlling said damping portion following said ionization portion.

11. The apparatus as recited in claim 8 wherein said oscillator means includes a ringing circuit, switch means controlling said ringing circuit and pulse generating means for controlling said switch means.

12. The apparatus as recited in claim 11 wherein said switch means includes first and second controlled rectifiers, and said ringing circuit includes capacitance means connected between said first and second controlled rectifiers.

13. The apparatus as recited in claim 12 wherein said ringing circuit includes a transformer having a primary winding connected to said capacitance means and said first controlled rectifier.

14. The apparatus as recited in claim 13 wherein said transformer includes a secondary winding connected with said ionizing electrode means.

15. The apparatus as recited in claim 14 wherein said oscillator means includes a positive terminal of a DC source, said ringing circuit includes a resistor connected between said positive terminal and said second controlled rectifier, said primary winding being connected between said positive terminal and said first controlled rectifier, and said capacitance means including a capacitor connected between said resistor and said primary winding.

16. The apparatus as recited in claim 15 wherein said controlled rectifiers each have anode, cathode and gate electrodes, said anode of said first controlled rectifier being connected to said primary winding, said anode of said second controlled rectifier being connected to said resistor, said cathodes of said first and second controlled rectifiers being connected to a reference potential and said gates of said first and second controlled rectifiers being connected to receive separate trigger pulses from said pulse generating means, and said capacitor being connected between said anodes of said first and second controlled rectifiers.

17. The apparatus as recited in claim 8 wherein said ionizing electrode means includes a plurality of corona discharge electrodes disposed on a single side of the insulative material.

References Cited UNITED STATES PATENTS 3,391,314 7/1968 Carter 317-262 A 3,414,769 12/1968 Hoffman 3172 F LEE T. HIX, Primary Examiner U.S. Cl. X.R. 317--262 A, 4

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,716,754 Dated February 13, 1973 Inventor(s) Guy Paul WEBER E AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Heading, insert the following: I

--Claims priority, ap

A pl'ication France, September 24, 1970, 70/34560.---

Signed and Scaled this I si t m [SEAL] x D y f March 1976 Arrest:

23TH C. MA SON C. MARSHALL DANN esnng Ojjzcer Commissioner oj'Patenzs and Trademarks UNITED STATES PATENT OF F ICE CERTIFICATE OF CORRECTION Patent No. 3,716,754 Dated February 13, 1973 Inventor(s) Guy Paul WEBER ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Heading, insert the following:

"Claims priority, application France, September 24, 1970, 70/34560.

Signed and Scaled this I t th [SEAL] D3) of March 1976 Attest:

:33! :Q c. MARSHALL DANN 9 mg i Cvmmissimwroj'lalents and Trademark 

